8 



now of a deep chestnut-brown colour, and is crossed by three cream- 

 coloured stripes. The black spots have almost disappeared ; in 

 specimens where the dry- season character is extreme, they have 

 entirely vanished. Now comes the question, can we explain this 

 remarkable seasonal change on the analogy of Precis .' I think there 

 is little doubt that we can. Looking at the underside of the dry- 

 season form, we should at first sight be inclined to think that it 

 must be conspicuous. But when we find from observation in the 

 field that the butterfly is accustomed to settle with its wmgs closed 

 over its back, so as to show the underside, among dried grass 

 stems, we see that the peculiar striping is really well adapted to aid 

 concealment. In the wet season the striping is lost altogether in B. 

 gotziiia, partly so in B. ilithyia. The butterfly now presents a rough 

 resemblance to some of the small Acraeas, and probably derives some 

 protection from its likeness to that distasteful group of insects. 

 That this supposition is not merely imaginary appears likely from 

 some experiment? made by Mr. Marshall with captive baboons. We 

 have, therefore, in BU/blia the same kind of alternation as ia Precis, 

 between the cryptic disguise of the dry season and the warning or 

 mimetic aspect of the wet. 



There are other cases in which the same principle will help us to 

 an explanation. In many parts of the world the dry soil which is 

 left exposed after the withering of vegetation is reddish in colour. 

 It is constantly found that the undersides of butterflies belonging to 

 certain groups assume in the dry season a reddish hue, which cor- 

 responds closely with the peculiar character of the soil. The African 

 white butterflies with purple tips, belonging to the genus Teracolus, 

 are good instances of this defensive coloration. One of these but- 

 terflies, settling on the ground and closing its wings over its back, 

 becomes very difficult to distinguish from its surroundings, as I know 

 from personal experience in South Africa. In the wet season a few 

 of these butterflies retain the red-earth suffusion of their under- 

 surface, but the greater number lose it. It is not always possible to 

 assign any particular significance to the wet-season aspect of the 

 insects now referred to; it may be, however, that some of them are 

 mimics, while others may exhibit what are spoken of as " directive 

 marks," features, that is, which serve to divert the attacks of enemies 

 to non-vital parts, and so permit the escape of the butterfly at some 

 sacrifice of its personal appearance. In all the cases, however, it is 

 to be observed that the method of cryptic resemblance, which is 

 probably the most efficacious mode of defence, is the one employed 

 during the perilous period of the dry season. At other times of the 

 year, when the struggle is less severe, the protection becomes cor- 

 respondingly less complete. Another point to be observed is that 

 the defensive coloration, whether cryptic or mimetic, is mainly con- 

 centrated on the under-surface, that being the surface which is 

 exposed when the insect is at rest. This seems to indicate that the 

 enemies against whose attacks it is most necessary to be provided, 



